Multi-unit printing presses that print color images superimposed upon each other to form a complete multi-color image are known in the art. To form a clear multi-color image, it is necessary to have precise registration between the various units of the printing press.
Devices utilized to vary the phase relationship from unit-to-unit in a multi-unit press for the purpose of registration are known in the art. Also, devices utilized to circumferentially register a printing plate with its associated blanket are known in the art. None of these devices however work in cooperation with each other to register one printing unit to another printing unit while minimizing non-print gap displacement between printing plates and their associated blankets.
Partial registration can be accomplished by utilizing a unit-to-unit phaser adjustment assembly to change the printing phase of an upper and lower printing couple of one unit to that of another unit. Also, partial registration can be accomplished within each printing unit by utilizing an upper and lower circumferential adjustment assembly to rotate the upper and lower plate cylinders with respect to their associated blanket cylinders.
The printing press is made ready for a printing run by setting each of the printing units to a mechanical zero position. As a web is printed on, an operator will examine the final printed image and will adjust the press, unit-by-unit, to register the image printed by one unit to that printed by another unit until all the units are in register. As the web continues to run during the printing process, further adjustments are made by the operator. These adjustments are necessitated by variances in paper properties, the amount of ink being applied to the paper, the amount of water applied to the paper, the amount of web tension and web elasticity. As further adjustments are made by the operator, it is possible for the gap in a printing plate to be advanced or retarded beyond the gap in its associated blanket. Also, when the operator makes unit-to-unit adjustments or circumferential adjustments within a unit, he must stop the press and mechanically advance or retard the cylinders or unit drive gears.
The problem with making adjustments in narrow gap cylinders is compounded, since any circumferential movement causes an increase in non-print length.